Asus UEFI/BIOS options - How to boot from DVD?

To get the DVD drive to show up in the boot menu, you might need to go into the BIOS (actually (U)EFI Settings) and enable Legacy (BIOS) Mode or the UEFI Compatibility Support Module (CSM) or similarly worded option:

(Screenshot of Asus Zenbook Prime UX31A-DH51 BIOS with CSM disabled.)

(Screenshot of Asus K55A BIOS with CSM enabled.)

Note: You might also have to disable both Boot / Fast Boot and Security / Secure Boot Control.